1. Field of the Invention
The present invention is related to a device which compresses still image data in accordance with a JPEG (Joint Photographic Expert Group) algorithm and records the compressed image data in a recording medium and, also, to a device which reads the compressed image data from the recording medium and expands the compressed image data to reproduce the still image.
2. Description of the Related Art
A standard algorithm, for the encoding of high resolution images and the transfer of that information through telecommunication transmission channels, has been recommended by the JPEG. In order to enable a large-scale data compression, the baseline process of the JPEG algorithm breaks down the original image data into components on a spatial frequency axis using a two-dimensional DCT process. Thereafter, the data expressed on the spatial frequency axis is quantized by using a quantization table. The quantized data is then encoded using a Huffman table.
The encoded (or compressed) image data can be expanded by carrying out a process, which is the inverse of the compression process described above, so that the original image data can be reproduced. Namely, the compressed image data is decoded, subjected to a dequantization process, using a quantization table, and finally, subjected to a two dimensional inverse discrete transformation, so that the original image data is reproduced.
At the moment, however, even if there is a copyright on the original image, for example, the compressed image data of the original image, which is recorded in the recording medium, is still, fully, reproduced if an image expansion is carried out using a conventional image expansion device.